The present invention relates to a method of detecting interference conditions of a radar device. The present invention also relates to a radar device.
There are numerous applications for radar devices in various fields of the industry. For example, the use of radar sensors is possible for short-range sensors in motor vehicles.
Essentially, a sending antenna in such radar devices emits electromagnetic waves. When these electromagnetic waves strike an obstacle, they are reflected and received by another antenna or the same antenna after being reflected. The received signals are then sent to a signal processing and analyzing unit.
In motor vehicles, for example, radar sensors are used for measuring the distance from targets and/or the relative velocity with respect to such a target outside the motor vehicle. Targets include, for example, parked vehicles or vehicles driving in front, pedestrians, cyclists or devices in the vicinity of the vehicle.
FIG. 1 is a schematic block diagram of a radar device having a correlation receiver according to the related art. A transmitter 300 is prompted by a pulse generator 302 to send a transmission signal 306 over antenna 304. Transmission signal 306 also strikes a target object 308, where it is reflected. Reception signal 310 is received by antenna 312. This antenna 312 may be identical to antenna 304. After receiving reception signal 310 by antenna 312, the signal is sent to receiver 314 and then supplied over a unit 316 having a low-pass filter and analog-digital conversion to a signal analyzer 318. The special feature of this correlation receiver is that receiver 314 receives a reference signal 320 from pulse generator 302. Reception signals 310 received by receiver 314 are mixed with reference signal 320 in receiver 314. Through correlation it is possible to determine, for example, the distance of a target object on the basis of the time lag from sending to receiving the radar pulses.
It is possible to operate between 4 and 16 such sensors, for example, on a vehicle. The sensors are arranged in space in such a manner that they have practically no mutual influence on one another. However, problems may occur in approaching other vehicles, as in a parking procedure or in stop-and-go driving. It is also possible that interference may also occur due to other wireless services, thus creating false targets in this manner. Such faulty detection of a false target is a disadvantage and may even cause risks during driving operation.
The present invention relates to a method of detecting interference conditions of a radar device, having the following steps: detecting irregularities in reception of signals, deactivation of the transmission branch, and detection of the presence or absence of target signals. If irregularities in the reception part, e.g., very rapidly changing targets, high-speed targets or targets with distances that change suddenly, are detected as part of the method according to the present invention, it is assumed that this is due to interference. Likewise, interference may also involve the sensor being blind, i.e., not detecting any targets at all. In these cases, the transmission branch of the radar device is shut down or, in more general terms, transmission of a transmission signal by the radar device is prevented. However, the correlation pulses are still sent to the mixer in the reception branch. The method according to the present invention determines whether target information is still being detected when the transmitter is deactivated. If this is the case, then it is determined that this is due to interference. It is thus possible to infer whether target information is faulty by detection of irregularities and performing a subsequent check.
Following detection of the presence of target signals, they may be eliminated on a software basis. This is possible in particular when static information is available, e.g., the information that a target is at a certain distance.
The method according to the present invention, however, may also be refined by eliminating the target signals, after their presence has been detected, by changing the mid-frequency of the radar device. This variant is used in particular for eliminating deterministically variable targets. A periodic or chaotic shift, for example, may be considered for changing the mid-frequency.
It may also be useful for the method according to the present invention to be performed in such a manner that after the presence of target signals is detected, they are eliminated by changing the pulse repetition frequency of the radar device. In this manner it is also possible to alter the radar device so that false targets are no longer detected, but real targets are still taken into account in the same manner.
Following detection of the presence of target signals, they may be eliminated by a notch filter. This may be beneficial if the interference is monochromatic or almost monochromatic. The interference frequencies are eliminated by the notch filter, so that radar operation is ultimately free of interference.
The method according to the present invention may be refined so that following detection of the presence of target signals, they are eliminated by pulse coding. For example, switching from pulse modulation to frequency modulation is one option. It is also possible to code the pulses by a PN coding method (PN=pseudo noise).
The method may also be improved upon beneficially so that following detection of the presence or absence of target signals, a continuous carrier signal is sent to a mixer in the reception branch, and the interference carrier frequency is determined by detuning the continuous carrier signal. This may be advantageous if sporadic signals are present. Due to the continuous carrier at the mixer in the reception branch, the received signals may be converted to a low frequency, e.g., in a range below 2 GHz. The interference carrier frequency may be determined by detuning the frequency.
In a comparable manner, the method may also be performed so that following detection of the presence or absence of target signals, the interference carrier frequency is determined by tuning a PLL source. Providing such a PLL source in the reception branch makes a variable carrier dispensable. However, an increased circuit complexity is necessary in the respective frequency range, e.g., in the range of 2 GHz.
The measurement may be declared invalid in the case when the interference signals are not eliminated. If the interference targets are not eliminated by the measures performed as part of the method according to the present invention, the entire measurement is discarded, so that this method ultimately permits a reliable determination of true signals and elimination of false targets.
The present invention also relates to a radar device having an arrangement for detecting irregularities in reception of signals, an arrangement for deactivating the transmission branch and an arrangement for detecting the presence or absence of target signals. The advantages of the method of detecting interference conditions of a radar device may be implemented with such a radar device.
This radar device may be beneficial if, following detection of the presence of target signals, the target signals may be eliminated on a software basis. In particular, faulty static information may be eliminated with such a configuration of the radar device.
The radar device according to the present invention may be improved upon in that following detection of the presence of target signals, they may be eliminated by altering the mid-frequency of the radar device. The mid-frequency may be changed periodically or chaotically. This may eliminate deterministically variable targets.
In an example embodiment of the radar device, it may also be provided that, following detection of the presence of target signals, they may be eliminated by altering the pulse repetition frequency of the radar device. This is another variant for eliminating false targets, but a change in pulse repetition frequency is performed here as an essential measure.
Following detection of the presence of target signals, it is also possible for these signals to be eliminated by a notch filter. Such a radar device may eliminate monochromatic interference in particular.
In another example embodiment of the radar device according to the present invention, it may be provided that, following detection of the presence of target signals, they may be eliminated by pulse coding. Different modulation methods may be used for pulse coding, either individually or in combination.
The radar device may be refined by the fact that, following detection of the presence or absence of target signals, a continuous carrier signal is sent to a mixer in the reception branch and the interference carrier frequency may be determined by detuning the continuous carrier signal. Since sporadic signals cannot be eliminated through the changes in the signals described, the radar device may be configured so that the received signals are converted to a low frequency, e.g., in a range below 2 GHz, by a continuous carrier at the mixer in the reception branch. The interference carrier frequency may be determined by detuning the frequency.
In another example embodiment, however, it may also be possible that following detection of the presence or absence of target signals by tuning a PLL source, the interference carrier frequency may be determined. This measure is comparable to detuning the continuous carrier frequency on the mixer in the reception branch. However, due to the fact that a PLL source is provided, a variable carrier frequency may be omitted.
In the case when the interference signals are not eliminated, the measurement may be declared invalid. If the measures to eliminate the interference signals fail, the entire measurement is discarded. The radar device thus ultimately permits a reliable determination of real targets and elimination of false targets.
The present invention is based on the finding that, due to the detection of irregularities in reception of signals and due to the subsequent testing of target signals when the operation of the radar device is altered, it is possible to detect and eliminate interference signals. This interference detection may also be used for multisensor platforms for mutual synchronization or frequency tuning of the sensors among one another. The present invention may be used to advantage in the automotive field so that ultimately driving convenience and safety are improved.